In the operation of nuclear power plants, there are several important problems that significantly increase the cost of operations and maintenance. Some of these significant problems are: inherently low thermal efficiency, erosion-corrosion fuel storage and waste disposal limitations, equipment maintainability and reliability concerns as well as the limited fuel availability and the expensive requirements of storing spent fuel.
Various approaches have been tried to solve these problems separately, but few of the existing methods attack more than one of these concerns at a time.
Currently, in nuclear power plants (both pressurized water reactors or boiling water reactors), steam at the inlet of the turbine is saturated. This results in lower turbine efficiency and intensive erosion-corrosion problems.
There have been several attempts to use single or multiple fossil reheaters to treat the steam of a operating nuclear power plant. However, while higher steam temperatures due to fossil heating between the low pressure turbine stage and the high pressure turbine stage have been achieved, higher efficiency still has not been demonstrated. One such attempt is U.S. Pat. No. 5,361,377 to John A. Miller. The Miller heat exchanger method and apparatus of treating the steam claims an increase in efficiency by use of a fossil fired reheater. A problem with this method is that the fossil reheater still consumes fuel in a process that is inefficient in itself. In other words a big part of the heat from the burning of the fossil fuel goes up the stack. A process is needed that produces electricity, and utilizes the waste heat from that process to treat the steam in an efficient manner.
Mixing of the steam going from the LP stage to HP stage of the main turbine with high enthalpy steam is a solution that brings all of these advantages.
It is generally recognized that for mixing to be done in non-isothermal fluids, in boundary flow conditions, a pipe length of about 50 diameters is required. In a typical nuclear power plant the typical main steam pipe outside diameter is approximately 0.8 meter. This would require a pipe of 40 to 50 meters in length to achieve through mixing. Therefore, a more efficient means of mixing is needed to mix the steam from a heat recovery boiler with main steam.
It is therefore an object of the instant invention to treat the steam prior to entering the HP stage of the main turbine, then again before entering the LP stage by mixing the nuclear steam with high enthalpy steam from an efficient process.